Generally, a charge air cooler (an intercooler) is used with an internal combustion engine having a supercharger. When intake air is compressed by the supercharger, intake air temperature increases while this compression process. Since combustion characteristics may get worse due to excessive increase of the intake air temperature, the intake air temperature is reduced by the charge air cooler. Note that, if not specified, a term “supercharger” in the present application means a supercharger in a broad sense including a turbocharger and so on [a supercharger in a narrow sense means a supercharger that does supercharging by utilizing a drive force of a drive source (an combustion engine)].
As a typical charge air cooler, known are an air-cooling type charge air cooler that does cooling by utilizing a flow of outside air involved with a vehicle, and a water-cooling type charge air cooler that does cooling by utilizing refrigerant (coolant, cooling water). Know is a water-cooling type charge air cooler with a structure in which a heat exchanging section that forms a coolant flow path is produced independently and then the heat exchanging section is inserted into a case. By flowing intake air through the case, the cooling water and the intake air exchange heat therebetween.
In a water-cooling type charge air cooler, intake air is cooled by a low temperature side cooling flow path that is provided with a sub-radiator and separated from an engine cooling flow path (a high temperature side cooling flow path) provided with a radiator for cooling an engine. Target temperature of intake air to be supplied to the engine is about 45° C. and that is relatively low. Therefore, intake air cannot be cooled sufficiently by the engine cooling flow path. Consequently, intake air is cooled by the low temperature side cooling flow path.
In order to cool intake air to about 45° C., it is needed that refrigerant flowing through the low-temperature side cooling flow path should be cooled to about 40° C. For cooling the refrigerant to about 40° C., the sub-radiator must be made big in size to enhance its cooling capacity. Since installation freedom degree of the sub-radiator made big in size is restricted, the sub-radiator is generally located in front of the radiator (for example, Japanese Patent Application Laid-Open No. 2006-522893 [Patent Document 1] and Japanese Patent Application Laid-Open No. 2007-514890 [Patent Document 2]).